Engine ignition systems may include a spark plug for delivering an electric current to a combustion chamber of a spark-ignited engine, such as a gasoline engine, to ignite an air-fuel mixture and initiate combustion. Spark plug fouling may occur wherein a firing tip of the spark plug insulator becomes coated with a foreign substance, such as fuel or soot. Soot-fouled spark plugs include a carbon build-up on an electrode of the spark plug, whereas wet-fouled spark plugs include liquid fuel build-up around the electrode. Spark plugs may become wet-fouled due to engine flooding, for example. The engine may flood due to rich fueling during extreme temperature weather conditions, when an operator depresses/pumps the gas pedal repeatedly during cranking, or due to excess fuel inside the cylinders (e.g., due to a degraded fuel injector). When the spark plugs become wet-fouled, they are unable to produce a spark across the electrode, thus delaying or preventing engine start. In some instances, engine flooding may cause a frustrated vehicle operator to continue cranking the engine until the battery drains. Further, vehicle emissions may be increased due to repeated unsuccessful cranks while the engine is flooded.
One example approach to address spark plug wet-fouling is shown by Dudar in U.S. Pat. No. 9,790,874. Therein, upon detection of a fouled spark plug prior to an engine start, ambient air may be drawn in though the evaporative emissions control (EVAP) system and routed to one or more engine cylinders. The ambient air may be drawn in by operating a pump of the EVAP system and the air may be heated via a heater coupled to a fuel vapor canister of the EVAP system. The flow of heated ambient air through the engine cylinders facilitate in drying the spark plugs.
However, the inventors herein have recognized potential issues with such systems. As one example, the fuel vapor canister of the EVAP system may be saturated with fuel vapor and by drawing in ambient air through the fuel vapor canister of the EVAP system, an undesired amount of fuel vapor may be routed to the engine cylinders during an engine non-combusting condition. Since the fuel vapors are not being combusted, there may be an increase in vehicle evaporative emissions. Further, the fuel vapors may impede drying of the wet spark plugs. Cranking the engine without providing additional airflow to dry the spark plugs may be inefficient, resulting in increased engine starting times. The increased engine starting times may increase vehicle operator frustration as well as consume excess battery charge.
In one example, the issues described above may be addressed by an engine method comprising: in response to flooding a combustion chamber of a spark ignition engine with fuel during an engine start attempt, shutting off fuel delivery to the combustion chamber, activating a heating element of a catalyst coupled to an exhaust passage of the engine, and spinning the engine in reverse to flow air heated by the heating element to the combustion chamber via the exhaust passage. In this way, by reverse rotating the engine and routing heated air from an electrically heated catalyst to the engine cylinders, fouled spark plugs may be dried.
In one example, in an electrically heated catalyst (EHC), a heating element coupled to the catalyst may be activated to heat the catalyst during engine start conditions in order to expedite catalyst light-off. Upon detection of a wet-fouled spark plug, the engine may be spun, unfueled, in a reverse direction via an engine motor. Due to the reverse rotation of the engine, ambient air may be drawn into the engine system via the exhaust passage. The heating element coupled to the EHC may be activated to heat the ambient air flowing to the engine cylinders via the EHC. The heated air upon entering the engine cylinders may dry the fouled spark plugs. After routing heated air through the engine cylinders for over a threshold duration, spark plugs coupled to one or more cylinders may be activated to generate spark. If a characteristic secondary waveform is detected for each spark that is generated, it may be confirmed that the spark plugs are dry. Upon confirmation that the spark plugs are dry, reverse rotation of the engine may be discontinued and the fueling may be resumed for engine start.
In this way, by opportunistically using existing engine components, such as an electrically heater catalyst, the need for additional equipment or external intervention for spark plug drying may be reduced or eliminated. By reverse rotating the engine, the drop in exhaust pressure may be utilized to draw in ambient air and dry out the spark plug. The technical effect of utilizing heated airflow for drying the spark plugs is that multiple spark plugs may be dried simultaneously as the engine is rotated and cylinder valves of each cylinders open and close periodically. Overall, wet-fouled spark plugs may be dried faster than when no additional airflow is provided, decreasing the engine starting times and thereby decreasing vehicle operator frustration.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.